1. Field of the Invention
The present invention provides an earthquake-resistant structure for existing wood frame buildings, and, in particular, to truss members which prevent both the building cripple walls from collapsing during an earthquake and for securing the building to its foundation.
2. Description of the Prior Art
In order to keep various independent elements within a structure intact during an earthquake, adequate supports and seismic bracing (anti-movement brace used to prevent adverse sway or movement in the event of an earthquake) must be installed. Without such seismic bracing, the independent movement can result in such elements breaking away from their installed position causing severe damage to the structure.
Many states, including California, passed laws mandating that all new buildings, residential or commercial, be constructed with certain seismic bracing features incorporated therein. However, owners of existing structures were not required to upgrade the structures to incorporate seismic bracing. In view of the fact that earthquake damage caused to structures which were reinforced was less severe than non-reinforced structures, legislation has been recently proposed that mandates that existing structures must be brought up to existing code requirements.
Existing code requires houses to be bolted to their foundation. However, when bolting down an older home, there is only about 2 1/2 inches to about 3 inches of concrete on each side of the bolt. In many cases, the footings are slightly decomposed, making them vulnerable to seismic damage due to cracking and/or splitting of the foundation at the bolt location. In those homes built with cripple walls, bracing was typically accomplished by using strips of plywood. However, the plywood strips tend to rot due to moisture and termites, making the bracing ineffective.
Typical of the prior art seismic brace system installations are those disclosed in U.S. Pat. No. 4,065,218 to Biggane which discloses a channel iron having an articulated connection at each end, one end being connected to a building element, the other end being connected to the item supported; U.S. Pat. No. 4,441,289 to Ikuo et al. which discloses a method for providing earthquake reinforcement for existing buildings which uses a compression brace on the beam pillar structure of a building in a diagonal direction to the structure so as to apply a pre-compressive stress to the compression brace; U.S. Pat. No. 2,089,023 to Hahn which discloses a structural member designed to resist longitudinal stresses in a wall structure to prevent distortion and deformation of the wall, the member being arranged for attachment to a sill or foundation by suitable anchors when used as a foot piece or for attachment to rafters or joists when used as a header; and U.S. Pat. No. 4,615,157 to Murray which discloses a system for damping oscillations in building floor joists.
Although the various structures noted hereinabove provide techniques for reinforcing buildings against seismic damage, they are relatively costly and not specifically adapted to reinforce existing wood frame buildings or structures built before foundation anchor bolts were required by municipal building codes.
What is therefore desired is to provide a method for reinforcing existing wood frame structures against seismic stresses and, in particular, to prevent both the structure cripple walls from collapsing during an earthquake and to secure the structure to its foundation.